1. Field of the Invention
The invention relates to a hydraulic drilling device comprising a driving head mountable at the upper end of a drill rod, a hydraulic motor for rotating the drill being fitted coaxially about the driving head.
2. Description of the Prior Art
In known drill hammers, the hydraulic motor is secured laterally to the drive head and drives the drill rod via a pinion fastened to the motor shaft and a crown gear connected to rotate the drill. With such a drive means, because of the crown gear, pinion and lateral motor arrangement, the drive head has a substantial radial projection, which makes its use in mining inconvenient. As known, it is necessary in mining to work in narrow tunnels and, to advance a shaft or gallery, the bore holes should be as close as possible to the gallery wall. The greater the radial dimension of the drill head, the more difficult is it to drill a bore hole directly adjacent to the gallery wall. Therefore, the holes are frequently bored at an inclination relative to the gallery axis. Moreover, the weight of the pinion and crown gear assembly significantly increases the weight of the drill hammer.
It is an object of the invention to provide a drilling device of the type described, wherein the radial extension of the drill rotation means is relatively small, which is of lighter weight than known drilling hammers, which does not require a crown gear assembly, and which can be manufactured simply and at low cost.